The present invention relates to a high speed continuous decorator machine for decorating cylindrical containers such as can bodies and, more specifically, relates to a mandrel wheel assembly comprising apparatus for moving a mandrel spindle having an improperly seated can or no can thereon out of printing relationship with an associated blanket wheel to avoid printing of the mandrel spindle exterior surface.
Can printing (decorating) machines, especially high speed continuous can printing machines, operate by the impingement of a rotating, image-carrying blanket wheel and an oppositely rotating can carrying mandrel wheel assembly. The blanket wheel comprises an endless blanket which is at least as wide as the length of the cans being printed. The blanket carries a series of wet ink images circumferentially spaced on its resilient periphery. The mandrel wheel assembly comprises a mandrel wheel mounted with a series of circumferentially spaced, rotatable mandrel spindles over which cans are fitted. The cans rotate on the mandrel wheel into registry and contact with the images on the surface of the blanket wheel. Each mandrel spindle generally includes structure for removing cans from or drawing cans onto the mandrel spindle.
During high speed can printing, a can will occasionally fail to properly seat on a mandrel spindle or a gap will occur in the continuous can infeed to the machine causing one or more mandrel spindles not to have a can received thereon. In such circumstances, it is necessary that the mandrel spindle not be moved into contact with the blanket wheel to prevent the mandrel spindle surface from being printed. A number of different mechanisms have been utilized in the past to provide such a "skip-print" feature.
Hartmeister et al., U.S. Pat. No. 3,655,853 issued May 30, 1972 describes a continuous printer and skip-printer mechanism comprising a plurality of blanket holder segments on a rotated drum successively movable into and out of printing position, a stationary cam, a cam follower on each segment, and operative connections including a withdrawable bridge member between the cam follower and each blanket holder segment for moving the segment into printing position. An air cylinder responsive to a malfunction signal actuates a pivotally mounted trigger and connecting rod which are part of skip-print means for withdrawing the bridging member from the operative connections between the cam follower and each blanket holder segment, thereby producing a gap in the operative connections and preventing movement of the segment into printing position when malfunction occurs, without interrupting subsequent printing operations.
Zurick, U.S. Pat. No. 3,851,579 issued Dec. 3, 1974 describes a trip mechanism for a continuously rotating can printing or coating machine having rotatable can shaft supports, which is operable to displace the support from a print blanket. The trip mechanism includes an eccentric sleeve between the shaft and a bore which is rotatable with the bore and about the shaft. In a normal position, the sleeve holds the shaft in position to effect contact between a can mounted thereon and the print blanket. A detector provides a trip signal in response to the absence of a can. A trip cam and trip cam follower pair are provided, one of which is mounted on the eccentric sleeve. The trip cam is thrown from a normal print to a trip position in response to a trip signal. The trip pair is positioned to engage one another when the cam is in the trip position to cause rotation of the sleeve whereby the shaft and can support are displaced away from the print blanket.
Sirvet, U.S. Pat. No. 4,037,530 issued July 26, 1977 describes a pocket mandrel wheel having mandrels mounted on mandrel spindles that pivot to move the mandrels laterally to prevent the mandrels from contacting an associated printing wheel. The mandrel spindles are attached to the mandrel wheel by a pivot arm that controls the radius of the mandrels line of motion as the mandrel wheel rotates. The pivot arm causes the mandrel spindle to rotate the mandrel in response to an electronic system that detects improperly seated cans on the mandrels. The pivot arm rests against an interposer block having a recessed step, and the mandrel is withdrawn when the block is moved in response to a signal from the electronic system so that the pivot are rests against the recessed portion of the block. The movement of the block is controlled by a mechanical system that moves the pivot are away from the block prior to the time when the mandrel may be tripped.
The prior art designs, because of the relatively large number of moving parts, have proven to be expensive to construct and to maintain. The numerous moving parts of such prior art designs also create dimensional tolerance related problems in a system where registry between a can carrying mandrel spindle and image carrying blanket wheel must be exact. Yet another problem with prior art designs has been that the trip mechanism for the skip-print system must be actuated prior to the time that a mandrel spindle is in the immediate vicinity of the blanket wheel in order for the skip-print system to have sufficient time to move the mandrel spindle from its ordinary, blanket wheel contacting path to a path which is spaced apart form the blanket wheel. In such a system, the detection device which senses the absence of a can or an improperly seated can on a mandrel spindle is necessarily positioned a substantial distance "upstream" of the blanket wheel contact area. As a result of this upstream positioning such a detection device cannot sense a can which becomes unseated from a mandrel spindle at a point downstream of the detection device but upstream of the blanket wheel contact area. In extremely high speed machines this problem is accentuated because the detection device "looks at" a can/mandrel spindle seating arrangement prior to the time that the can seating (transfer of the can body from a pocket opposite a mandrel spindle to the mandrel spindle) is completed. Thus the seating detection device is required to predict whether or nor a given can will seat on a mandrel spindle, rather than actually observing the proper seating or lack of proper seating. Since such "predictions" are necessarily less accurate than an observation of the can/mandrel spindle seating arrangement immediately prior to contact of the can with the blanket wheel, misseated cans are occasionally printed. Such printing results in an improper image transfer known in the trade as "partial litho". Similarly, cans which are properly seated on the mandrels are occasionally not printed because of an erroneous prediction by the seating detection device.
Another problem encountered with a number of existing mandrel spindle skip-print mechanisms is that, due to relatively infrequent operation of the skip-print mechanism within an otherwise dynamic system, the bearings of certain parts associated with the skip-print mechanism deteriorate through a phenomenon known as "bernelling" or "fretting corrosion".
It would be generally desirable to provide a mandrel wheel assembly which prevents a mandrel spindle from engaging a blanket wheel except when a can body is properly seated thereon. It would also be desirable to provide a mandrel wheel assembly which provides accurate registry between can bodies and a blanket wheel and which is relatively inexpensive to adjust and maintain as compared to existing mandrel wheel assemblies. It would further be desirable to provide a mandrel wheel assembly which allows relatively longer loading time for seating a can body on a mandrel spindle than present machines without decreasing machine operating speeds. It would still further be desirable to provide a mandrel wheel assembly having highly accurate can seating detection apparatus. It would yet further be desirable to provide a mandrel wheel assembly with a skip-print apparatus which is not subject to bernelling.